PHP/Javascript/Jquery -Selecting a dropdown item should dynamically display another

I have code for autosuggestion while typing in a text box written in Javascript and PHP. When I start typing a number I get a list of matching numbers and I'm able to select one of them with the mouse click. Now I have an other text box which should display a list of numbers based on the selection from the first textbox. I have no clue on how to do this. It would be great if you provide me with the sample code for the same. Please help me out.